The cytopathologic effects of exposure to polychlorinated biphenyl compounds (PCBs) have varied considerably with the dosages and mixtures of isomers administered, with duration of exposure, and with the species that have exhibited toxic effects. The liver has been the organ studied most carefully for histo- and cytopathologic changes because hepatomegaly has often resulted from PCB toxicity, because the agranular endoplasmic reticulum, the site of drug metabolizing enzymes in hepatocytes, proliferates in response to PCB exposure, and because hepatic tumors have been produced in rodents after long-term exposure. Available evidence indicates that PCBs often affect the histologic and cytologic organization of other tissues, especially epithelia and their derivatives, that have moderate to rapid rates of cell renewal. No studies thus far have attempted to determine whether PCBs directly affect cell division, cell differentiation, or both of these processes. In the proposed experiments, the effects of exposure to Aroclor 1254, a widely used askarel of PCBs and a persistent environmental pollutant, will be compared in two sites -- cutaneous sebaceous glands and gastric glands of the stomach -- whose cytology is known to be altered after exposure to PCBs. The effects on rates of cell division in these sites will be determined by radioautography, those on cell differentiation with cytochemical and morphometric techniques. Data thus obtained will be correlated with ultrastructural observations of these sites gained from transmission and scanning electron microscopy.